cluster: save to the region cache when pending-peers or down-peers change (#3462)

[ti-srebot]

cherry-pick #3462 to release-4.0
You can switch your code base to this Pull Request by using git-extras:

# In pd repo:
git pr https://github.com/tikv/pd/pull/3471

After apply modifications, you can push your change to this PR via:

git push git@github.com:ti-srebot/pd.git pr/3471:release-4.0-b1ba2d01663f

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What problem does this PR solve?

close #3456

What is changed and how it works?

• Before: save to the region cache when pending-peers or down-peers exists
• After: save to the region cache when pending-peers or down-peers change

Check List

Tests

• Unit test

Related changes

• Need to cherry-pick to the release branch

Release note

• save to the region cache when pending-peers or down-peers change

[ti-chi-bot]

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[ti-srebot]

@HunDunDM you're already a collaborator in bot's repo.

[HunDunDM]

/merge

[ti-chi-bot]

@HunDunDM: It seems you want to merge this PR, I will help you trigger all the tests:

/run-all-tests

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[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: 504232a

[ti-chi-bot]

@ti-srebot: Your PR was out of date, I have automatically updated it for you.

At the same time I will also trigger all tests for you:

/run-all-tests

If the CI test fails, you just re-trigger the test that failed and the bot will merge the PR for you after the CI passes.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.

[codecov]

Codecov Report

Merging #3471 (797dcde) into release-4.0 (ff6c0d2) will decrease coverage by 0.50%.
The diff coverage is 100.00%.

@@               Coverage Diff               @@
##           release-4.0    #3471      +/-   ##
===============================================
- Coverage        75.10%   74.60%   -0.51%     
===============================================
  Files              209      209              
  Lines            19790    19809      +19     
===============================================
- Hits             14864    14778      -86     
- Misses            3586     3693     +107     
+ Partials          1340     1338       -2     

Flag	Coverage Δ
unittests	74.60% <100.00%> (-0.51%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
server/cluster/cluster.go	78.10% <100.00%> (-2.68%)	⬇️
server/core/region.go	92.38% <100.00%> (+0.29%)	⬆️
server/core/region_option.go	83.33% <100.00%> (+0.40%)	⬆️
server/statistics/store_collection.go	58.53% <0.00%> (-34.96%)	⬇️
pkg/errs/errs.go	75.00% <0.00%> (-25.00%)	⬇️
server/schedulers/shuffle_hot_region.go	56.88% <0.00%> (-11.93%)	⬇️
server/region_syncer/server.go	79.38% <0.00%> (-9.93%)	⬇️
server/kv/etcd_kv.go	69.56% <0.00%> (-7.25%)	⬇️
server/region_syncer/client.go	78.74% <0.00%> (-4.73%)	⬇️
pkg/dashboard/adapter/manager.go	81.52% <0.00%> (-3.27%)	⬇️
... and 13 more

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[HunDunDM]

/rebuild